The organocatalytic aldol reaction between acetone and α-substituted β-keto esters is presented. The α-unsubstituted or α-chloro ethyl acetoacetates failed to react with acetone when l-proline was used as catalyst. l-Proline or other optically pure pyrrolidine derivatives catalyzed the direct aldol reaction of acetone and α-fluorinated β-keto esters affording δ-keto-β-hydroxy-α-fluoro esters in high yields. Both the α-fluoro- and α,α-difluoro-β-keto esters functioned as aldol acceptors in these reactions. High ee values, up to 83% coupled with low diastereoselectivities were obtained in the reaction of ethyl 2-fluoroacetoacetate. Our study revealed a novel extension of the scope of the organocatalytic direct aldol reaction catalyzed by chiral organic bases, being the first report in which an asymmetric organocatalytic fluoroketone-ketone aldol addition has been described.
- Direct aldol addition
- Ethyl 2-fluoroacetoacetate
ASJC Scopus subject areas
- Process Chemistry and Technology
- Physical and Theoretical Chemistry